1. Field of the Invention
The present invention relates to a full color digital image forming apparatus such as a full color copying machine.
2. Description of the Prior Art
An image processor which reads a document image is provided in a full color digital image forming apparatus such as a full color digital copying machine or connected to a digital printer, and it processes a digital document image for reproduction. A full color digital image forming apparatus is used to reproduce various types of documents such as a full color image, a monochromatic image, a character document, a photograph, a map, a dot image, or a printed photograph. In order to reproduce such documents appropriately, it is desirable to change image processing in the digital image forming apparatus according to the document type. Previously, a user selects document type with an operational panel, and the image processor processes a document image according to the selection.
However, the manual selection is troublesome for a user. Further, if an automatic document feeder is used and documents including various document types are set in the document feeder, manual selection is impossible. In such a case, it is desirable that the image processor determine the document type automatically, and both full color documents and monochromatic color documents have to be dealt in a unified way in the automatic document type.
Previously, automatic exposure (or background deletion) adopted in a conventional copying machine is performed only in a black copy mode because a reproduced color image in a full color copy is affected when automatic exposure is performed on a full color image in full color copy mode. Recently, automatic color selection mode became available in order to improve operation of a color copying machine and to shorten copying time. In the automatic color selection, it is determined if a document put on a platen is a black-and-white document or a color document, and a color image forming operation or a black image forming operation is performed automatically according to the decision. Automatic exposure mode, however, can be adopted automatically only when the document is determined to be a black-and-white document.
However, if automatic exposure mode is selected according to the decision by the automatic color selection, the following problems occur: Although a document such as a printed image of a newspaper or a magazine including color images and black character images is determined as a color document in the automatic color selection, when such a document is copied, it is necessary to prevent reproduction of an unnecessary image on a reverse side of the sheet of the document. Further, a document such as a magazine often has a background having a color such as cream, and when the cream background is reproduced in a color copy of the document, this unnecessarily wastes toner.
Further, the quality of copy is improved recently by using region discrimination such as a region of black characters after extracting features of a document for performing a processing according to the result of the region discrimination. For example, if a region of black characters is detected, edge emphasis may be performed to improve image quality. Even in a full color mode, processing such as black character discrimination is introduced, and a document including color and black images can he reproduced sharply. However, this is not yet complete, so that a user maintains a quality of a copy according to the type of a document determined by the user, not by using the region discrimination. Then, it is needed that a user adjusts an image control manually when a color copy is generated, and this operation is troublesome for a user. Thus, though the automatic color selection is introduced for the ease of a user and for shortening a copying time, it may complicate the operation of a user and increase a copying time. Further, it is a problem that an image adjustment of a color copy and a selection of a document type are difficult. For example, there are various types of documents such as a full color document, a monochromatic document, a character document, a photograph, a map, a dot image document, and a printed photograph. Thus, the image adjustment and the selection of the document type may not result a copy as expected by the user. What is needed is to control background automatically irrespective of the document type in a unified way.
Further, when an automatic document feeder is mounted on a color copying machine, image adjustment cannot be performed if color documents and black-and-white documents are mixed. Then, image adjustment and document mode selection cannot be performed for each document.